Pathogenesis of respiratory infections due to influenza virus: implications for developing countries.

The influenza viruses have an important and distinctive place among respiratory viruses: they change antigenic character at irregular intervals, infect individuals of all ages, cause illnesses characterized by constitutional symptoms and tracheobronchitis, produce yearly epidemics associated frequently with excess morbidity and mortality, and predispose the host to bacterial superinfections. Much is known about influenza viruses, but their role in respiratory infections among children in developing countries is poorly understood, and the risk factors that lead to the excess morbidity and mortality have not been identified clearly. Among the many risk factors that may be important are alterations in host immunity, malnutrition, prior or coincident infections with other microorganisms, inhaled pollutants, and lack of access to medical care. There is a great need for research that can establish more precisely the role these and other unidentified factors play in the pathogenesis of influenza infections in children in the developing world.